Living near the limits: Effects of interannual variation in food availability on diet and reproduction in a temperate primate, the Taihangshan macaque (Macaca mulatta tcheliensis)

Nutrient intake of animals is influenced by an interplay of external and internal factors, such as food availability and reproductive state, respectively. We used the nutritional geometry framework to analyze individual-based data on energy and nutrient intake in relation to reproductive state in a population of rhesus macaques (Macaca mulatta tcheliensis), which live in a harsh high-latitude habitat, the Taihangshan mountains of China, and exhibit strong reproductive seasonality. We combined data over a 3-year period on food availability, diets, reproductive output, and components of maternal investment to understand how Taihangshan macaques respond to variation in food availability and nutrition in reproduction. Our results show there was high interannual variation in availability of an important staple source of fat and carbohydrates (nonprotein energy), seeds of oak (Quercus spp). Despite this variability in seed availability skewing the dietary macronutrient ratios considerably (from 12.96% to 30.12% dietary energy from protein), total metabolizable energy intake was maintained across years during pregnancy. Lactating females had higher mean daily energy intakes than pregnant females. As in pregnant females, energy intake was maintained constant across years, but only when seed availability enabled the contribution of available protein to energy intake to be maintained between 15.32% (2013) and 17.97% (2015). In 2014, when seeds were scarce, lactating females had a shortfall in energy intake compared with 2013 and 2015. This corresponded with a reduction in the number of females giving birth (11 out of 23), but there was no interannual difference in survival rates. Compared to 2013 and 2015, in 2014 females had greater weight loss (drew on body reserves), moved less, and spent more time nursing their offspring. We discuss implications of these results for range limitation in Taihangshan macaques.

Experimental evolution demonstrates evolvability of preferential nutrient allocation to competing traits in response to chronic malnutrition

Investigating the evolutionary origins of disease vulnerability is an important aspect of evolutionary medicine that strongly complements our current understanding on proximate causes of disease. Life-history trade-offs mediated through evolutionary changes in resource allocation strategies could be one possible explanation to why suboptimal traits that leave bodies vulnerable to disease exist. For example, Drosophila melanogaster populations experimentally evolved to tolerate chronic larval malnutrition succumb to intestinal infection despite eliciting a competent immune response, owing to the loss of their intestinal integrity. Here, I test whether evolved changes in resource allocation underlies this trade-off, by assaying preferential allocation of dietary protein towards growth and tissue repair in the same populations. Using two phenotypic traits, regeneration of intestinal epithelium post-pathogenic infection and body weight, I show that in accordance with the dynamic energy budget theory (DEB) dietary protein acquired during the larval phase is allocated to both growth and adult tissue repair. Furthermore, by altering the ratio of protein and carbohydrates in the larval diets I demonstrate that in comparison with the control populations, the evolved (selected) populations differ in their protein allocation strategy towards these two traits. While the control populations stored away excess protein for tissue repair, the selected populations invested it towards immediate increase in body weight rather than towards an unanticipated tissue damage. Thus, I show how macronutrient availability and their allocation between traits can alter resistance, and provide empirical evidence that supports the 'mismatch hypothesis', wherein vulnerability to disease is proposed to stem from the differences between ancestral and current environment.

Testing the Effects of DL-Alpha-Tocopherol Supplementation on Oxidative Damage, Total Antioxidant Protection and the Sex-Specific Responses of Reproductive Effort and Lifespan to Dietary Manipulation in Australian Field Crickets (Teleogryllus commodus)

The oxidative stress theory predicts that the accumulation of oxidative damage causes aging. More generally, oxidative damage could be a cost of reproduction that reduces survival. Both of these hypotheses have mixed empirical support. To better understand the life-history consequences of oxidative damage, we fed male and female Australian field crickets (Teleogryllus commodus) four diets differing in their protein and carbohydrate content, which have sex-specific effects on reproductive effort and lifespan. We supplemented half of these crickets with the vitamin E isoform DL-alpha-tocopherol and measured the effects of nutrient intake on lifespan, reproduction, oxidative damage and antioxidant protection. We found a clear trade-off between reproductive effort and lifespan in females but not in males. In direct contrast to the oxidative stress theory, crickets fed diets that improved their lifespan had high levels of oxidative damage to proteins. Supplementation with DL-alpha-tocopherol did not significantly improve lifespan or reproductive effort. However, males fed diets that increased their reproductive investment experienced high oxidative damage to proteins. While this suggests that male reproductive effort could elevate oxidative damage, this was not associated with reduced male survival. Overall, these results provide little evidence that oxidative damage plays a central role in mediating life-history trade-offs in T. commodus.